Aristotle was an Athenian philosopher, whose work remains foundational to the Western philosophical tradition. Aristotle was Plato's student, just as Plato was Socrates'. Aristotle lived from 384 BCE to 322 BCE, and in his lifetime he explored philosophy, literature, mathematics, and the natural sciences, among seemingly endless other topics. He taught at the Lyceum in Athens, and his institution came to be known as the Peripatetic school, as Aristotle would walk while he lectured to his pupils. Of course, his most famous student was Alexander the Great of Macedon.
Politics is Aristotle's most complete surviving treatise on political philosophy. You will notice that his writing style is very different from that of Plato. Recall that Plato's philosophy took the form of dialogues. Aristotle, on the other hand, formulates arguments based on his own thoughts and the beliefs of others. You should try to approach philosophical texts like Socrates would approach an interlocutor: interrogate every step of the argument and discover the underlying assumptions and, possibly, contradictions or ambiguities.
As you read Politics, pay special attention to Aristotle's views on human nature and how this affects social organization.